Picornaviruses are non-enveloped, positive single-stranded RNA viruses with an RNA genome 7.2-8.5 Kb long. These viruses are very small and globular in shape with a size of about 22˜30 nm, and were first identified a long time ago. Among the viruses belonging to the family Picornaviridae are enteroviruses including rhinovirus, poliovirus, coxsackievirus A, coxsackievirus B, and echovirus, and hepatitis A virus.
The diseases that picornaviruses cause are varied, ranging from respiratory diseases to digestive diseases, to circulatory diseases and to dermal diseases, examples of which include poliomyelitis, paralysis, acute hemorrhagic conjunctivitis, viral meningitis, hand-foot-and-mouth disease, vesicular disease, hepatitis A, myositis, myocarditis, pancreatitis, diabetes, epidemic myalgia, encephalitis, flu, herpangina, and foot-and-mouth disease. However, there are no therapeutics for curing these diseases. Most of the drugs under development are uncoating inhibitors. Viruses belonging to the family Picornaviridae cause various diseases including the aforemented respiratory diseases, which evoke hygienic, social and economic issues. Picornaviruses are the main causative agents of waterborne diseases. Being very stable and difficult to disinfect, the RNA viruses incessantly cause related diseases.
Human rhinoviruses (hRV) have been recently associated with the majority of asthma exacerbations, and are known to exist even in bronchial tissues of many stable asthma patients. Comparison of respective bronchial mucosa biopsy specimens taken from asthma and non-asthma patients showed significantly higher frequencies of detection of human rhinoviruses in the lower respiratory tract of asthma patients, compared to non-asthma patients. It has also been reported that there is correlation between the presence of rhinovirus and the clinical severity of asthma. In addition, rhinoviruses cause chronic obstructive pulmonary disease, pneumonia, sinusitis, and otitis media as well as asthma.
Rhinoviruses are the main causative of the common cold while enterovirus-induced diseases include meningitis, respectory tract infection, etc. Extensive effort to provide vaccination against poliovirus has significantly reduced the onset of poliomyelitis worldwide, but there are still reports of cases of the disease in Niger, Nigeria, Egypt, India, Parkistan, and Afghanistan. Hepatitis A is now possible to control to some degree thanks to vaccines for hepatitis A viruses. However, no vaccines for coxsackieviruses, echoviruses, or rhinoviruses have been developed, thus far.
Particularly, coxsackievirus B is a main cause of myocarditis, which may develop, in serious cases, into idiopathic dilated cardiomyopathy, which requires heart transplantation
Enviroxime derivatives are considered the most promising candidate with a broad anti-enterovirus- and anti-rhinovirus activity. Enviroxime interferes with the synthesis of plus-strand RNA by binding to the virus protein 3A that is required for the formation of RNA intermediates in the virus reproduction (Heinz B A and Vance L M: J Virol, 1995, 69(7), 4189-97). In clinical studies, however, the compound was observed to have insignificant or few therapeutic effects, with the concomitant detection of bad pharmacokinetics and unwanted side effects (Miller F D et al.: Antimicrob Agents Chemother, 1985, 27(1), 102-6).
The protease inhibitor AG 7088 has been developed on the basis of the knowledge about the fine structure and function of the viral protease 2C. In the cell culture in the nanomolar concentration range, AG 7088 has an effect against 48 rhinovirus types and coxsackievirus A21, B3, enterovirus 70 and echovirus 11 (Pattick A K et al.: Antimicrobila Agents Chemother, 1999, 43(10), 2444-50).
Thanks to the clarification of the molecular structure of the viral capsids, the preconditions for a purposeful design of capsid blockers, the “WIN substances”, have been obtained (Diana G D: Curr Med Chem 2003, 2, 1-12). They inhibit the adsorption and/or the uncoating of rhinoviruses and enteroviruses. Some of the WIN substances have a highly specific effect only against individual genera or virus types of the picornaviruses. Other derivatives inhibit the replication both of rhinoviruses and enteroviruses. Arildone, disoxaril and pirodavir belong, for example, to the WIN substances. These compounds showed very good antiviral effects in the cell culture. However, a poor solubility (arildone), low bioavailability (arildone and disoxaril), a rapid metabolization and excretion (disoxaril and WIN 54954) as well as side effects, such as skin rash (WIN 54954), made a clinical application impossible.
Pleconaril, a kind of WIN substance, has a very good oral bioavailability and after its binding to the hydrophobe pocket in the viruscapsid, it inhibits the penetration of rhino-, echo- and coxsackieviruses (Pevear D C et al.: Antimicrob Agents Chemother 1999, 43(9), 2109-15; McKinlay M A et al.: Annu Rev Microbiol 1992, 46, 635-54). Therefore, pleconaril is potentially effective against a broad spectrum of virus diseases, ranging from the common cold to the viral meningitis or myocarditis. Resistances were observed for rhinoviruses, enterovirus 71 and coxsackievirus B3 (Ledford R M et al.: J Virol 2004, 78(7), 3663-74; Groarke J M et al.: J Infect Dis 1999, 179(6), 1538-41). However, the proven therapeutic effect was not sufficient for the registration of pleconaril (Picovir, Viropharma, USA) as an agent for the treatment of rhinovirus infections in the USA. In March 2002, a corresponding application was refused by the Food and Drug Administration (FDA) because therapy success was too low and side effects were observed.
BTA-798 was found to have higher antiviral activity than pleconaril, as evaluated in vitro and in vivo with rhinoviruses, and is now being under a clinical test (Ryan, J. et al. Antiviral Res [18th Intl Conf Antiviral Res (April 11-14, Barcelona) 2005] 2005, 65(3): Abst LB-11).
However, no antiviral drugs that have gained approval for use in the treatment of entero- or rhinoviruses have been developed, so far.
Leading to the present invention, intensive and thorough research into effective virustatics against picornaviruses including coxsackie-, entero-, echo-, polio-, and rhinoviruses, culminated in the finding that novel indanone derivatives exhibit highly inhibitory activity against picornaviruses including coxsackie-, entero-, echo-, polio-, and rhinoviruses.